SORCE
August 2001 Project Summary
The EOS SORCE mission is still on schedule and within budget. Launch
is scheduled for July 31, 2002. Progress made on the SORCE Mission
integration at LASP during the past month includes the completion
of the SOLSTICE A shake, the delivery of the SOLSTICE A to SURF
(Synchrotron Ultraviolet Radiation Facility) for final calibration,
and the "extermination" of the SORCE MU FPGA (microprocessor
unit flight programmable gate array) bug. The end-to-end LPT (limited
performance test) testing for the XPS and TIM instruments has been
completed.
Activities at Orbital Science Corporation include the integration
of the CEUA (central electronics unit A), APE1 (attitude power electronics
1), PRE (power regulator electronics) and the NF (nonflight) Fuse
Assembly on the spacecraft bus. In addition the CEUB, MTB (Magnetic
Torquer Bar) X & Y, and TAM (Three Axis Magnetometer) B have
also been installed on the spacecraft bus. The end-to-end LPT (limited
performance test) testing for the XPS and TIM instruments has been
completed.
The TIM Hitchhiker schedule has been lowered in priority to accommodate
the completion of SORCE. The spacecraft "gyro" descope
discussions continue. SORCE Red Team activity is in progress and
the Aerospace Corporation has received the Red Team proposal from
Orbital Sciences Corporation. The entire document is being edited
for its submission to NASA by September 2001. SORCE continues to
routinely monitor and adjust schedules to expedite instrument fabrication.
Currently the spacecraft bus is one month behind schedule. Orbital
Sciences Corporation is reorganizing their build plans in order
to find additional build slack. Slack in Phase D is being pulled
forward to cover phase C. This process has reduced slack for Phase
D, but current slack margins although tight, are acceptable.
The top
concerns facing the SORCE program are:
1. Concern
from NASA Code 570 for a "gyroless" SORCE flight mode.
|
2. Tight
instrument testing schedules.
3. Late delivery of the flight SORCE MU (microprocessor unit).
4. Tight SIM characterization and calibration
schedules.
5. Diminishing contingency funds.
6. Delayed instrument software testing due to late MU build
7. Replacement of Interpoint Power Converters, and discovery that
the power converters do not meet radiation specifications. A discussion
of the situation follows.
Interpoint
Power Converters
Over the past two months, SORCE has encountered problems concerning
Interpoint power converters. At power on, the power converters
were delivering transient power spikes to the instrument GCIs
(generic channel interfaces). A softstart circuit has been designed
to eliminate the problem. Replacement parts that do not exhibit
the spiking were procured to replace the questionable units and
thereby solve the initial problem. Then, SORCE discovered that
the power converters did not meet radiation specifications. The
parts SORCE is employing, SMHF2805S and SMHF2815D, appear not
to function at the specific dose rate. Parts failures have occurred
at 4 to 6 K rad. The parts failures are due to a CMOS MOSFET driver
chip - TC4426. The Electronic Parts Engineering Office of JPL
(Jet Propulsion Lab) is working with Crane Interpoint Corporation
to resolve the problem. A GIDEP (government industry data exchange
program) Problem Advisory has been written by Interpoint defining
the issue. It has not yet been officially released by Interpoint,
but its identifying number will be MT2-P-01-01. SORCE currently
holds the unofficial copy of the document. SORCE has some options
for dealing with the radiation problem. The questionable parts
could be shielded using tantalum or tungsten in order to arrive
at <2Krad TID. This approach will add mass and may present
PWB (printed wire board) structural problems. Additional analysis
will be required to fully define the problem and find a solution.
Crane Interpoint speculates they
|
